1. Field of the Invention
The present invention relates to a synchronization acquiring method for matching the phase of a spreading code, which is used to spread data at a base station so as to enable the mobile station to communicate by radio with the base station, with the phase of a spreading code, which is used at the mobile station to de-spread input data that is used to de-spread the input data input from the base station, and a synchronization acquiring apparatus for carrying out the synchronization acquiring method. The act of matching the phase of the spreading code used at the base station with the phase of the spreading code used at the mobile station is called synchronization.
2. Description of Related Art
Two types of operations for performing a synchronization at the mobile station are known. One of them is a synchronization acquiring operation and the other is a synchronization tracking operation.
When a power source is turned on at the mobile station, the mobile station performs a synchronization acquiring operation. Conventionally, the sliding correlating system has been used for the synchronization operation. In the sliding correlating, the phases of a spreading code to be multiplied with the input data are slid so as to be de-spread the input data supplied from the base station, a de-spread result is obtained for each of the phases, and a phase that maximizes the correlation value is obtained from the de-spread result. When the power source is turned on at the mobile station, the mobile station slides the phases of the spreading code by entire bits of the spreading code in the sliding correlating system so as to perform the above-described synchronization acquiring operation. In such a synchronization acquiring operation, the number of phases of the spreading code to be slid by the sliding correlating system is large. Therefore, it requires a long time to perform the synchronization acquiring operation.
The mobile station performs a synchronization tracking operation after the synchronization acquiring operation. In the synchronization tracking operation, the mobile station maintains the state of synchronization between the phases of the spreading code, on which the synchronization acquiring operation has been performed, and the input data that is serially input to the mobile station. For example, a conventional synchronization tracking apparatus in which a PLL circuit (Phase Locked Loop Circuit) is used is able to realize such a synchronization tracking operation.
In general, the mobile station shifts to a sleep state when the mobile station is put into a waiting state while performing a synchronization tracking operation in order to reduce power consumption. While the mobile station is in the sleep state, the mobile station periodically monitors for any input data supplied from the base station while maintaining the state of inactivity. When no data is supplied from the base station, the mobile station remains in the sleep state. If any input data is received during the sleep state, the mobile station shifts from the sleep state to an active state. The mobile station performs a synchronization acquiring operation again to shift to the active state. The same sliding correlating system is used in the synchronization acquiring operation. When the mobile station shifts from the sleep state to the active state, the mobile station repeats exactly the same operation that the mobile station performed when the mobile station last shifted to the active state. Therefore, the mobile station requires a long length of time to perform the synchronization acquiring operation.
Given these problems, it is an object of the present invention to provide a synchronization acquiring method capable of reducing the length of time required to perform in wireless communication a synchronization acquiring operation when the mobile station shifts from a sleep state to an active state and a synchronization acquiring apparatus capable of performing such a synchronization acquiring method.
In order to achieve the above-stated objective, a synchronization acquiring method according to the embodiments of present invention has the following three steps. In, the first step multiple correlation values are obtained between the input data supplied from a base station to the mobile station and multiple phases of a spreading code multiplied with the input data in the mobile station before the mobile station transits from the active state to the sleep state, multiple phases of the spreading code that correspond to the correlation values are determined, and the multiple phases are stored. In the second step, phases of the spreading code multiplied with the input data are determined using the phases obtained when the mobile station transits from the sleep state to the active state. In the third step, correlation values between the input data and the phases of the spreading code multiplied with the input data are obtained using the phases of the spreading code determining in the second step.
Preferably in the second step, it is judged whether the mobile station has been moved or not while the mobile station was in the sleep state when the mobile station transits from the sleep state to the active state. If the mobile station has remained at rest, the phases of the spreading code are determined using the multiple phases stored in the first step. If the mobile station has been moved, the size of a range, over which the phases of the spreading code are slid, are determined to be equal to the entire range that corresponds to the length of the spreading code.
In order to achieve the above-stated objective, a synchronization acquiring apparatus according to embodiments of the present invention has a correlation storing unit which obtains correlation values between the input data supplied from the base station and the spreading code multiplied with the input data and stores the correlation values and the phases of the spreading code that correspond to the correlation values, and an operation control unit which judges whether a synchronization acquiring operation has been completed or not based on the correlation value stored in the correlation storing unit, sends the phases to synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed, performs a control so as to repeat the synchronization acquiring operation when the operation control unit judges that the synchronization acquiring operation has not been completed, and receives the multiple phases stored in the synchronization tracking apparatus to control the correlation storing unit using the phase stored in the synchronization tracking apparatus and the phase differences between the phases stored in the synchronization tracking apparatus when the mobile station transits from the sleep state to the active state.
Preferably, the correlation storing unit of the synchronization acquiring apparatus according to the present invention has a first spreading code generating unit which, when a first starting phase is input from a phase control unit, generates a spreading code sliding a phase from the first starting phase over a prescribed range and generates the spreading code sliding a phase over a prescribed range that corresponds to the length of the spreading code when a control signal is input from a control unit, a first de-spreading unit which multiplies the spreading code generated by the first spreading code generating unit to the input data and outputs first demodulated data, a second spreading code generating unit which, when a second starting phase is input from the phase control unit, generates a spreading code sliding a phase from the second starting phase over a prescribed range and generates the spreading code sliding a phase over a prescribed range that corresponds to the length of the spreading code when a control signal is input from the control unit, a second de-spreading unit which multiplies the spreading code generated by the second spreading code generating unit to the input data and outputs second demodulated data, a correlation generating unit which outputs correlation values between the input data and the spreading code based on the first demodulated data and the second demodulated data, and a first memory which receives phases of the spreading code that generates the peaks of the correlation values based on the correlation values from the first de-spreading unit and stores the correlation values and the phases of the spreading code. Also preferably, the operation control unit has a control unit which receives the correlation values stored in the first memory, judges whether the synchronization acquiring operation has been completed or not based on the correlation values, sends the phases stored in the first memory to a second memory installed inside the synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed sends a reset signal for repeating the synchronization acquiring operation to the first de-spreading unit and the second de-spreading unit when the operation control unit judges that the synchronization acquiring operation has not been completed, and reads at least two phases stored in the second memory of the synchronization tracking apparatus to output the phases and a phase difference between the phases when the mobile station transits from the sleep state to the active state, and a phase control unit which outputs the first starting phase and the second starting phase using the phases and the phase difference output from the control unit.
More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, an adder which calculates the sum of the first cumulative data and the second cumulative data, and an amplitude calculating unit which calculates the amplitude of the sum and outputs the amplitude as the correlation value.
More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has an adder which calculates the sum of the first demodulated data and the second demodulated data, an accumulating unit which accumulates the sum calculated by the adder to produce a cumulative sum and outputs the cumulative sum as cumulative data, and an amplitude calculating unit which calculates the amplitude of the cumulative data and outputs the amplitude as the correlation value.
More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, and an adder which calculates the sum of the first correlation value and the second correlation value. The correlation generating unit then outputs the sum obtained by the adder as the correlation value.
More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, a first square calculating unit which calculates the square of the first correlation value and outputs the square of the first correlation value as a first squared correlation value, a second square calculating unit which calculates the square of the second correlation value and outputs the square of the second correlation value as a second squared correlation value, and an adder which calculates the sum of the first squared correlation value and the second squared correlation value. The correlation generating unit then outputs the sum obtained by the adder as the correlation value.
More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, a first square calculating unit which calculates the square of the first correlation value and outputs the square of the first correlation value as a first squared correlation value, a second square calculating unit which calculates the square of the second correlation value and outputs the square of the second correlation value as a second squared correlation value, and an adder which calculates the sum of the first squared correlation value and the second squared correlation value. The synchronization acquiring apparatus further has a first additional memory which receives the phase of the spreading code that generates the peak of the first squared correlation value based on the first squared correlation value from the first de-spreading unit and stores the phase, and a second additional memory which receives the phase of the spreading code that generates the peak of the second squared correlation value based on the second squared correlation value from the second de-spreading unit and stores the phase. Moreover, the operation control unit has a control unit which receives the phase stored in the first additional memory and said phase stored in the second additional memory, sends the phase stored in the first additional memory and the phase stored in the second additional memory to the second memory installed inside the synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed, sends a reset signal for repeating the synchronization acquiring operation to the first de-spreading unit and the second de-spreading unit when the operation control unit judges that the synchronization acquiring operation has not been completed, and reads at least two phases stored in the second memory of the synchronization tracking apparatus to output the phases and a phase difference between the phases when the mobile station transits from the sleep state to the active state, and a phase control unit which outputs the first starting phase and the second starting phase using the phases and the phase difference output from the control unit.
More preferably, the first additional memory of the synchronization acquiring apparatus according to the present invention receives the phase of the spreading code that generates the peak of the first squared correlation value based on the first correlation value from the first de-spreading unit and stores the phase, and the second additional memory receives the phase of the spreading code that generates the peak of the second squared correlation value based on the second correlation value from the second de-spreading unit and stores the phase.